Adverse outcomes of sick leave due to mental disorders: prospective studies of discordant twin pairs

Abstract

Abstract Background Sick leave due to mental disorders is common. We investigated if sick leave due to mental disorders increased the risk of reoccurring sick leave, disability pension, unemployment, in- and specialized outpatient care, and mortality, using a co-twin design, taking genetics and shared environment (familial factors) into account. Methods The register-based open cohort studies contained twin pairs 18-64 years old discordant for sick leave due to a mental disorder. First, 2202 pairs were followed up to 8 years from the end of the sick leave spell for reoccurring sick leave, disability pension and unemployment. Second, 4979 twin pairs were followed up to 9 years from the beginning of the sick leave spell for death, inpatient and specialized outpatient care. Conditional Cox proportional hazard regression, adjusting for familial factors, was used to calculate Hazard Ratios (HR) with 95% Confidence Intervals (CI). Results Those with sick leave due to mental disorders had 3.64 (CI: 3.24-4.08) times higher risk of reoccurring sick leave the first two years and the first year, they had 12.24 (CI: 8.11-18.46) times the risk for disability pension. The risk of unemployment was 1.99 (CI: 1.72-2.31). The HR for inpatient care was 1.90 (CI: 1.66-2.17) among men but lower among women. For men the risk of outpatient care was higher the first 2 years (HR: 2.08, CI: 1.87-2.31), and for women the HR was 1.57 (CI: 1.47-1.68) for the whole study time. There was an increased risk of death among men (HR: 2.91, CI: 1.70-4.99), but not among women. Conclusions By adjusting for familial factors we could investigate if the same factors that predispose to sick leave due to mental disorders also predispose to morbidity, mortality and unemployment and hence explain the associations. But, sick leave due to mental disorders was associated with a higher risk of work related and health outcomes, independent of familial factors. The risks varied over time and differed among women and men.